Arbitrary Matrix rotations

Hi, I''ve been working on introducing myself to OpenGL programming and have realized that I''m a little lacking in the math department. I''m trying to work on a base class for objects on 3d space. This class would store the location and orientation of a specific object. My algebra is too rusty to hand;e quaternions just yet, so I''m using matrices. My question is this: what''s the equation for rotating a matrix around an arbitrary vector? Basically I need an explination of how glRotate works. Thanks in advance.